cheapest, safest and most simple way to power a led from 240V AC

[danrogers]

Hi all.

I would like to run a LED from a 240V AC supply. I need a simple way to indicate power.

I have opened a few things up over the years and found just an inline resistor. Is this method safe?

Thanks

 

[tvtech]

Hi Dan

A good place to start is to read this link :http://www.marcspages.co.uk/tech/6103.htm

Regards,
tvtech

 

[alec_t]

The safest way is to use a small mains-to-low-voltage transformer followed by a bridge rectifier feeding the LED via a current-limiting resistor.

 

[Experimentonomen]

The absolute safest and cheapest is to use a transformer based power supply like a wallwart or a laptop psu if the leds are of the higher power kind.

NEVER EVER NEVER NEVER NEVER NEVER NEVER NEVER EVER use a transformerless psu, these are a death trap.

 

[tvtech]

The absolute safest and cheapest is to use a transformer based power supply like a wallwart or a laptop psu if the leds are of the higher power kind.

NEVER EVER NEVER NEVER NEVER NEVER NEVER NEVER EVER use a transformerless psu, these are a death trap.

Hello Experimentonomen

Why the shouting?? You maybe got belted??

Remember simplicity and understanding what you are doing....

So now to light one little LED as an indicator...you need to make things complicated and expensive....

I am busy preparing a Tutorial on X2 Transformerless Power Supplies. Based on my circuitry. 4 Years of development and 1 Year of flat out testing to the extreme.

Please bear in mind if designed correctly they don't bite. Many learned people simply don't understand how they work....

It's time to educate people once and for all

Regards,
tvtech

 

[JimB]

NEVER EVER NEVER NEVER NEVER NEVER NEVER NEVER EVER use a transformerless psu, these are a death trap.

Yes indeed!

Just like all those uninsulated wires running around with 400kV on them!

Only dangerous when not used correctly.

JimB

 

[Nigel Goodwin]

Only dangerous when not used correctly.

Considering one of the listed requirements was 'safest', it's perhaps not a good idea to suggest the least safe method possible? - where the LED is permanently live and potentially dangerous.

Nothing wrong with transformerless PSU's, but ONLY under particular specific circumstances - a perfect example would be a light dimmer, where it's already all live anyway.

 

[4pyros]

I need a simple way to indicate power.

I think in this case the transformerless power supply is acceptable solution providing its in a box with other live equipment.

 

[ronsimpson]

Neon bulb and resistor. You can get a plastic case with bulb and resistor inside. Can come panel mount.

 

[Nigel Goodwin]

Neon bulb and resistor. You can get a plastic case with bulb and resistor inside. Can come panel mount.

Which is probably what the OP has seen, seeing as he says he's only seen a single resistor feeding the light (which wouldn't work with an LED).

 

[tvtech]

Hi Nigel

It's all about informing people about choices. And explaining things along the way.

That way they learn more. And respect circuits more...because they...know more.

So no more blind LED from Mains things they open up and wonder how it works.

I know this is a controversial topic....but it needs to be thrashed out and put in the open. Even learned Ratch does not really understand how it all works.

And I was not going to be suckered into a "debate" last night when he started with me....LOL

All I know is ETO at least has the balls to allow a subject like this to be discussed on this Forum. Instead of denying or prohibiting any discussion thereof..

One last thing: I will with EM's consent and the Legal powers that be publish my compete project here for all to see and learn. Everything from the PCB design to clearances and as to why things work so well. I need to finally stamp my foot and explain to people that Transformerless Power Supplies are not as bad as some make them out to be.

I need to get closure and understanding. Like I have said many times before...X2 supplies are unburstable if designed and built correctly.

Thanks for your time Nigel.

tvtech

 

[danrogers]

Thanks for the info guys, I'll have a read up when I get home. I forgot to say I need a simple (and small) solution so I can fit it into a tight space so a transformer is probably not a viable option

 

[ronsimpson]

I felt stupid suggesting NEON not LED . After Nigel's post I now think NEON is safer and has been used to 100 years.
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From the link in post #2: Multiple LED:

I know this is not really to the question. But. Why parallel LEDs in a 220V to LED circuit?
When paralleling LEDs you need more current thus a larger capacitor. (which is already very large)

The goal is to get from high voltage to low voltage. So series LEDs make more sense to me.

 

[alec_t]

Why parallel LEDs in a 220V to LED circuit?

It would provide some redundancy in the event of failure of one string; though the current in the remaining strings would increase by 50% each.

 

[Nigel Goodwin]

Thanks for the info guys, I'll have a read up when I get home. I forgot to say I need a simple (and small) solution so I can fit it into a tight space so a transformer is probably not a viable option

What is the unit?, and does it have low voltage supplies inside?, for that matter is it completely sealed and inaccessible if you were to use a permanently live light?.

 

[fezder]

a bit of off-topic, as it is led here in discussion, but as school, we powered 12v fan from 230v mains by using capacitor and diode, if i recall right. But, if it's wrong, don't blame me, blame teacher, he did it....

 

[tvtech]

Hello Fez

Now you see...everything is going to go off topic from here......

Behave yourself

Your Uncle,
tvtech

 

[tvtech]

Guys..never loose sight of the Original question:

Hi all.

I would like to run a LED from a 240V AC supply. I need a simple way to indicate power.

I have opened a few things up over the years and found just an inline resistor. Is this method safe?

Thanks

 

[audioguru]

An LED has only one polarity so a series diode must be used. The diode causes the LED to blink on and off at the mains frequency and it will appear dimmed.
To have a fairly bright LED its continuous current needs to be 20mA but must be 40mA when blinking at 50Hz. Then the resistor value is 238V/40mA= 5950 ohms but 6.2k is the nearest standard value. The heating in the resistor is 240V x 40mA for half the total time= 4.8W so a huge 10W resistor must be used and be in free moving ambient air (not enclosed) which is another serious shock hazard.

 

[alec_t]

An LED has only one polarity so a series diode must be used.

I challenge 'must'. That's one way, but the diode would need to be mains-rated. The other way is to use an anti-parallel diode which needs only a low voltage rating. This diode can advantageously be another LED to reduce the blink effect.